1. Field of the Invention
The present invention relates to a polishing machining apparatus and a machining method for machining a workpiece to be polished where a plurality of magnetic heads are arranged, and more particularly to an apparatus and a method for correcting a bend of the workpiece during the machining work.
2. Related Background Art
A thin film magnetic head to be used in a magnetic disc apparatus or the like is composed of parts obtained by machining a rod-shaped ceramic (hereinafter referred to as a ceramic bar) where a number of element parts made of a magnetic thin film or the like forming induction type magnetic converting elements, magnetic resistors (hereinafter referred to as MRs) elements or the like are formed in a line on a surface. Conventionally, in a batch type manufacturing process of parts for the thin film magnetic head, the ceramic bar where the plurality of element portions are formed is polished, and a process for machining a throat height or an MR height of each element part to a suitable level is executed. In general, in the magnetic disc apparatus, in order to stabilize the output characteristics from the magnetic head, it is necessary to keep a distance between the magnetic polar portions of the magnetic head and a surface of a recording medium to an extremely narrow constant distance. The value of the throat height or the like is used as an important parameter for defining this distance.
In the following description, the throat height means a length (height) of the tip end portion of the magnetic poles for performing the recording/reproduction of magnetic signals in such a head core part, i.e., the portion where the two magnetic poles face each other at a fine gap. Also, the MR height means a length (height) from the end portion of the MR element on the side facing the medium to the opposite end portion thereof. In order to make it possible to perform the suitable recording/reproduction of the signals, the values of the throat height, the MR height and the like must be selected suitably. In order to obtain the predetermined values, high precision is needed for the polishing work.
The ceramic bar is to be cut into respective element portions in a process thereafter. Each of the element portions constitutes a part of a magnetic head for the magnetic disc apparatus. In the case where the magnetic head is used in the magnetic disc apparatus, the ceramic portion becomes a slider that is to be lifted away from the magnetic disc by the blow pressure caused by the rotation of the disc. The element portion becomes a head core for performing the recording and/or reproducing the magnetic signals of the disc.
However, in general, the above-described ceramic bar has a strain, a bend or the like due to the stress caused by the formation of the element portion or the cutting operation from the ceramic substrate. It is therefore difficult to obtain the high machining precision only by fixing the ceramic bar and effecting the polishing work thereon. For this reason, a non-general polishing apparatus for performing the polishing work of the magnetic head with high precision in the form of the ceramic bar as disclosed in, for example, U.S. Pat. No. 5,620,356 or the like has been proposed. Also, the present assignee proposes some apparatus and some methods (Japanese Patent Application No. 11-162799 or the like).
An actual polishing method for the above-described ceramic bar will now be described.
First of all, the surface opposite the polishing surface of the ceramic bar, is fixed with adhesives or the like to a jig, and the surface to be polished of the ceramic bar is depressed through the jig against the polishing surface of a polishing base to perform the polishing work to the surface to be polished. The jig has a beam structure. A load is applied to several, three to seven, specific points on the jig from the outside of the jig to thereby cause deformation in the jig as a whole. Furthermore, this beam structure allows the portions fixed to the ceramic bar to be subjected to the complicated deformation by the balance adjustment of the above-described load, and the ceramic bar is bent simultaneously with the fixed portions to thereby make it possible to correct the bend or the like owned by the ceramic bar per se.
In the polishing work, in a predetermined element portion on the ceramic bar fixed to the jig, the values such as a throat height are measured optically or electrically to thereby obtain the difference between the measurement value and the target value, i.e., the amount of polished portion needed upon the measurement. The loads at the plurality of points are adjusted on the basis of the necessary polishing amount in the predetermined element portion obtained and the portion in the vicinity of the predetermined element portion, and the ceramic bar is polished while being deformed through the jig. These steps are repeated whereby the values such as the throat height and the like of all the elements formed in the ceramic bar fall within the predetermined range.
Opening portions into which pins or the like may be inserted are formed in the beam portion of the jig. The loads to the jig in the above-described process are given by transmitting the loads due to an actuator such as a low friction cylinder to the pins inserted into the opening portions of the jig through transmission parts. The adjustment of the loads to the jig is performed by adjusting the loads from this actuator, i.e., a drive amount of the actuator. Incidentally, Japanese Patent Application No. 10-178949 filed by the present applicant discloses a specific example of a jig for causing an effective deformation or a load distribution to the ceramic bar.
In a recording density in the current magnetic disc apparatus or the like, it is possible to make the values such as a throat height fall within an allowable range to some extent by a machining method of the magnetic head using the above-described jig. However, the high recording density is accelerated, and recently, the high precision of the throat height or the miniaturization of the elements are remarkable. It is difficult to make the values such as the throat height fall within the allowable range over the full length of the ceramic bar.
In the case where the allowable range of the values such as the throat height is narrowed, there is an approach to cope with this by, for example, increasing the application points of the loads that cause the deformation in the jig. However, since this leads to the increase of the number of the actuators that actually apply the loads or the transmission portions (application points) of the loads, if the actuators or the like used in the conventional apparatus are needed, it is difficult to actually perform this approach since the space for mounting the actuators or the like would be increased remarkably in view of the structure of the polishing apparatus. Also, in the case where the jig per se is miniaturized in accordance with the miniaturization of the elements, there would be a problem in that it is difficult to arrange the necessary number of the actuators or the like for applying the loads to the application points of necessary loads, and the like.
Furthermore, in the conventional polishing method, since the affect of the repulsive force from the polishing surface exists between the application point of the load and the beam or between the application points, it is impossible to sufficiently deform the ceramic bar. Accordingly, also in some conventional cases, depending upon the allowable range of the values such as a throat height, the values of the portion that may not be deformed could not fall within the allowable range. The approach to increase the number of the application points of the load and the number of the actuators for this problem has been attempted but there is a limit in the allowable range due to the above described problem.
Also, the conventional apparatus has three to seven actuators for deforming the jig in addition to the actuator for applying the main pressure for depressing the ceramic bar against the polishing surface and adjusting the load balance at both end portions in the longitudinal direction of the ceramic bar. However, actually, in order to bend the retainer portions to a necessary level, the three to seven actuators have to have a large stroke due to the necessary bend level and the actuators that always have the large stroke and occupy the large space in the structure are necessary as in the conventional case. Moreover, in order to make it possible to provide the complicated bend, the opening portion of the jig into which the pins cooperating with the actuators are inserted is increased to provide the form that may imparts a moment in the vertical direction, in the lateral direction and in the rotational direction with respect to the opening portion. In addition, it is necessary to effect the complicated drive control for each actuator. Accordingly, the conventional apparatus is not suitable for imparting the predetermined deformation amount to the very restricted portions of the ceramic bar.